I used fibre glass to create the mould. This involves using polyester resin and glass fibre mesh.
I also used a thixotropic agent to make the resin less runny.
The first step was to cover the sculpture in a layer of resin to make sure all of the detail was picked up. I simply dripped this on and pushed the resin into the details with a paint brush.
This is where the thickened resin was useful - for filling in overhangs and cavities.
Once the detail layer was finished a layer of glass fibre was added to give the mould structural strength.